This is a longitudinal study of recent onset IgA nephropathy. Thirty patients will be recruited. A combination of physiological study (clearance) and glomerular morphometry will be carried out longitudinally for five years to characterize the course of glomerular injury in this disorder. Principal components analysis will be used to predict the subset who exhibit progressive renal insufficiency, so that they can be targeted for a future trial of therapy. The longitudinal findings will be used to perform an analysis of statistical power for sample size. Clearance studies and biopsies require admission to and the resources of the GCRC.